130块样品的稀土元素含量、稀土分布模式、稀土特征值分析以及物源指数的计算表明,中亚热带网纹红土与北方黄土具有相似的稀土特征。网纹红土稀土元素平均含量(179.57μg/g)与地壳平均值(178μg/g)、北京郊区1998年12月大气粉尘稀土总量(177.97μg/g)以及两块中国黄土标样平均值(178.22μg/g)非常接近,稀土分布模式与风成沉积及UCC类同,轻稀土强烈富集,重稀土淋失,轻重稀土比值9.86~15.18,Ce元素正异常,物源指数<0.5。稀土元素特征指示,所研究的网纹红土的母质与黄土具有风尘相似性,而且风尘沉积后经历了较北方黄土更为强列的风化作用,其形成环境与古土壤和上新世红粘土接近。

The vermicular red earth is a kind of sediment which is widespread in middle sub-tropic zone. It is similar to the loess in grain size, mineral composition of clay, sedimentary texture and so on. This study compared the rare earth element (REE) feature of the vermicular red earth in southern China with that of the loess and other Aeolian deposits in northern China, in order to understand the origin of vermicular red earth better. The REE contents of the samples were measured by using the ICP-MS. And 130 samples which were collected from Jiujiang, Xinzi and Shahe in Jiangxi Province, Jinhua and Anji in Zhejiang Province, Zhuzhou in Hunan Province were analyzed. The results suggest that the vermicular red earth is similar to dust deposits in REE features. Vermicular red earth also originates from well-mixed and multi-cyclic sediments. (1) The average REE content of vermicular red earth is 179.57μg/g, greater than that soils of China, but it is near to those of earths crust (178 μg/g), the dust storm deposit of Beijing suburb in Dec. 1998 (177.97μg/g) and Chinese standard loess samples (CJ-1 and CJ-2, average in 178.22μg/g). (2) The vermicular red earth show a similar REE distribution pattern as that of the dust deposits in northern China. The curve is sharp from La to Eu, and flat from Eu to Lu. The Eu shows negative anomaly. (3) The LREE content of vermicular red clay is dominant, but the average content of HREE is 14.26mg/kg (the percentage is less than 10%), obviously lower than the loess (18.89mg/kg) and Pliocene red clay(18.57 mg/kg) in the northern China. The ratios of LEE and HREE range from 9.86 to 15.15, which is higher than those of the loess and Pliocene red clay. The element Ce appears highly positive anomaly. (4) The calculation of provenance index (P_i) indicates that vermicular red earth is similar to the loess and Pliocene red clay in the northern China in chemical component. (5) Compared with the white parts, the red matrix of vermicular red earth is characterized by the low concentration and low ratio of REE, but the distributing pattern is identical. In a summary, all of the above evidences from REE suggest that the vermicular red clay in studied areas may originate from dust and have the same source as the aeolian deposits in the northern China. The dust has suffered stronger weathering than loess during the accumulating process.